Laner Monika, Horta Bruno A C, Hünenberger Philippe H
Laboratory of Physical Chemistry, ETH Zürich, Zurich, Switzerland.
Eur Biophys J. 2014 Nov;43(10-11):517-44. doi: 10.1007/s00249-014-0982-9. Epub 2014 Aug 24.
The influence of the cosolutes trehalose and methanol on the structural, dynamic and thermodynamic properties of a glycerol-1-monopalmitate (GMP) bilayer and on its main transition temperature [Formula: see text] is investigated using atomistic molecular dynamics simulations (600 ns) of a GMP bilayer patch (2 × 8 × 8 lipids) at different temperatures in the range of 302 to 338 K and considering three different cosolute concentrations. Depending on the environment and temperature, these simulations present no or a single GL[Formula: see text]LC, LC[Formula: see text]GL or LC[Formula: see text]ID transition, where LC, GL and ID are the liquid crystal, gel and interdigitated phases, respectively. The trehalose molecules form a coating layer at the bilayer surface, promote the hydrogen-bonded bridging of the lipid headgroups, preserve the interaction of the headgroups with trapped water and induce a slight lateral expansion of the bilayer in the LC phase, observations that may have implications for the phenomenon of anhydrobiosis. However, this cosolute does not affect [Formula: see text] and its dependence on hydration in the concentration range considered. On the other hand, methanol molecules intercalate between the lipid headgroups, promote a lateral expansion of the bilayer in the LC phase and induce a concentration dependent decrease of [Formula: see text], observations that may have implications for the phenomenon of anesthesia. The occurrence of an ID phase in the presence of this cosolute may be viewed as an extreme consequence of lateral expansion. The analysis of the simulations also suggests the existence of two basic conservation principles: (1) the hydrogen-bond saturation principle rests on the observation that for all species present in the different systems, the total numbers of hydrogen-bonds per molecule is essentially constant, the only factor of variability being their distribution among different partners; (2) the densest packing principle rests on the observation that the effective volume per methylene group in the interior of the bilayer is only weakly sensitive to the environment, with values comparable to those for liquid (LC) and solid (ID) alkanes, or intermediate (GL).
利用原子分子动力学模拟（600纳秒），研究了共溶质海藻糖和甲醇对单棕榈酸甘油酯（GMP）双层膜的结构、动力学和热力学性质及其主要转变温度[公式：见原文]的影响。模拟对象为一个GMP双层膜片（2×8×8个脂质分子），温度范围为302至338K，考虑了三种不同的共溶质浓度。根据环境和温度的不同，这些模拟结果呈现出无转变、单一的液晶（LC）到凝胶（GL）、凝胶到液晶或液晶到交错（ID）相的转变，其中LC、GL和ID分别代表液晶相、凝胶相和交错相。海藻糖分子在双层膜表面形成一层包覆层，促进脂质头部基团之间的氢键桥连，保持头部基团与截留水的相互作用，并在液晶相中引起双层膜的轻微横向扩张，这些观察结果可能对脱水生物现象有影响。然而，在所考虑的浓度范围内，这种共溶质并不影响[公式：见原文]及其对水合作用的依赖性。另一方面，甲醇分子插入脂质头部基团之间，在液晶相中促进双层膜的横向扩张，并导致[公式：见原文]随浓度降低，这些观察结果可能对麻醉现象有影响。在这种共溶质存在下交错相的出现可被视为横向扩张的极端结果。模拟分析还表明存在两个基本守恒原则：（1）氢键饱和原则基于这样的观察，即对于不同系统中存在的所有物种，每个分子的氢键总数基本恒定，唯一的可变因素是它们在不同伙伴之间的分布；（2）最紧密堆积原则基于这样的观察，即双层膜内部每个亚甲基的有效体积对环境的敏感性较弱，其值与液态（LC）和固态（ID）烷烃或中间态（GL）的值相当。
